Impulse generator circuits



Feb,- 25, 1947.

A.,M. SKELLETT IMPULSE GENERATOR CIRCUITS Filed July 25, 1942 2/COLLECTOR 5 GRID @5251 i,

SHIELD 35 R2 .r/az

M/LLMMPERES I I I I I I l I I I I I I I0 .50 /00 1/0/20 [JO/40 [5016' II I I70 I80 I90 INPUT ix lNl/ENTOR A. M SKELLETT -ATTO EV Patented Feb.25, 1947 2,416,355 TMPULSE GENERATOR CIRCUITS Albert M. Skellett,Madison, Ni 1., assignor to' Bell Telephone. Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application July 25, 1942',Serial No. 452,332

18 Claims.

This invention is a continuation-in-part of my application Serial No.321,852, filed March 2, 1940, which matured into Patent 2,293,177, datedAugust 1-8, 1942. It relates particularly to impulse generator circuits.

The object of this invention is todevise an effective impulse generatoroperating onpure electron discharge and capable of sharp, sudden changesfrom the one condition of current flow to another.

The invention will be better understood from the following specificationtaken with the accompanying drawing, in which:

Figs. 1 and 2 are explanatory of the characteristics of a speech tubeshown in my earlier application;

Fig. 3 shows the circuit of one pulse generator disclosed in the saidearlier application; and

Fig. 4 is a modification thereof.

Fig. 5 shows a modification of Fig. 4.

In my earlier application I disclosed a particular form of tube makinguse of secondary emission. The essential elements of that tube are shownin Fig. 1 (which corresponds substantially to Fig. 3 of the parentapplication) which discloses a highly evacuated envelope containing acathode ll, a primary anode I9, and a control grid I8. In one portion ofthe anode there is an opening 3!] through which, as explainedhereinafter, electrons from the cathode may flow. The envelope alsocontains a deflector electrode 2! a collector grid 2|, a floating anode22, and a shield 36.

The cathode I1 is preferably of the equipotential type constituting asource of primary electrons when the cathode is'heated. The cathode maybe connected to the heater which would be of the filamentary typeenclosed within the cathode.

The input or control grid l8 surrounds and is coaxial with and spacedfrom the cathode, and preferably comprises a pair of axially extendingframe members'on which a large number of turns of closely paced, finewire is securely wound.

The anode I9 comprises a metallic cylinder that surrounds and is spacedfrom the grid and is coaxial with the latter. The aperture 30 may be anelongated slot that permits a preassigned percentage, for example, tenper centum, of the electrons emitted by the cathodev to pass through.

The deflector 26 comprises a bent metallic sheet spaced from the anodel9 and so disposed with respect to the aperture 30 that the electronspassing through the aperture are directed toward the deflector which maybe electrically connected to the cathode in order to be atcathode'p'otential. out through the aperture to follow trajectories ofthe character indicated by the dotted lines in Fig. 1, and to passthrough the collector grid 2i to impinge on the floating anode 22- whichis a secondary electron emitting source.

The collector grid 21 would ordinarily comprise. an. elongatedrectangular wire. frame, in.-

eluding aplurality of wires spaced. apart and arranged in. parallel toone another,. and disposed paraxially of the tube and in a plane at asubstantial angle'to the plane through the center of. thecathode. and.the center of the. aperture. 30.

* The. collector grid also includes a planar metallic or shieldportioniifi paced from. the anode. l9 and 7 extending substantiallyatrig-ht. angles to. the remainder, of the collector grid- Asex-plained.in my earlier application, the tube as thus; constructed may be utilizedas an. am.- plifier, a detector, an oscillator, or a modulator. It alsohas the characteristic. that it may be rendered. operative. ornon-operative. for such uses substantially instantaneously as the resultof applying to or removing a control potential, from the auxiliary anodeor the input. control grid. Furthermore, after the device; has beenrendered operative or triggered-on, the space current isandremainsundercontrolof the grid- I8 until the device:istriggered--ofi;. that is, the device may be employed in the usual wayin which the conventional three-element Vacuum tube or triode would beused;

The'trigger action of the device depends on the floating properties of.the auxiliary anode 22.

Fig. 2 shows a family of current versus potential characteristics ofthis floating anode for a tube constructed in accordance with theinvention. The different curves correspond to different potentials on:the. collector grid. As the-potential is increased, the currentpasses-through the zeroaxis twice. At each of these two points, thenumloer of primary electrons is equal to the number of. secondarieswhich are drawn off the surface. Iithe floating anode is at the higherzero potential, the external circuit'may' be entirely discon'- n-ectedand the. element. will float. in a perfectly stable manner at thisvoltage. At thev lower zero potential, however, the equilibrium isunstable 'If' the floating; anode is connected to ground,-

The deflector causes electrons that passthrough a high resistance,electrons will flow to it from the ground through this resistancebecause of its positive potential and these electrons will counteractthe effect of an equal number of secondaries simply by replacing thecharge carried away by the latter. On eifect of reducing the secondaryto primary ratio is that the second zero point or stable floatingpotential is reduced. The floating anode will now float at 'a potentialslightly less than it did when free. This new floating potential isdetermined by the intersection of the volt-ampere characteristic withthe line whose slope is equal to the load resistance. For example, thedotted lines R1 and R2 of Fig. 2 have the slopes of one megohm andtwo-tenths megohm, respectively, and the potentials of the point atwhich they cross the curves are of the "floating potentials for theseresistance values.

Resistances smaller than about 1.4 10 ohms do not intersect the curvesat all and the critical resistance is, therefore, near this value. It isgiven by the formula v so'that, in general, we have that where Em and Lmare the voltage and current of the negative maximum of thecharacteristic. The floating anode will not float at values ofresistance less than R0 for then the number of elec-, trons suppliedthrough the resistance will be in excess of the number of secondariesneeded to maintain the effective secondary-to-primary ratio at a valueequal to unit, and the floating anode will simply charge up negativelyand its potential will be brought to zero. These principles are utilizedto get off and on, or operate and non-operate, or block and unblock, ortrigger action in the vacuum tube.

The action of the device in a particular instance is shown in thecircuit arrangement of Fig. 3 (corresponding to Fig. 6 of my earlierapplication). The floating anode 22 is connected through the resistanceR and the input grid biasing battery C to the cathode. The input grid 18 is connected to one end of the secondary winding of an inputtransformer T1, the other end of the secondary winding being connectedto a contact engaging the resistance R and dividing it into two portionsR1 and R2. The primary anode i9 is connected with the cathode throughthe primary winding of the transformer T2 and the source, for example, abattery B, of anode The deflector 20 is connected to the' potential.cathode and the collector grid 2| is connected to the highly positiveterminal of a battery B. The values of R1 and Rzare such that theirtotal adds up to a value greater than Rs, preferably considerablygreater, one to five megohms being suitable.

Suppose that the cathode heater is turned on and'brought to operatingtemperature. The floating anode and the inner grid will all be at thenegative C potential and no electrons can flow through the tube. If,now, the potential of the floating anode is momentarily raised to avalue greater than the first zero potential (Fig. 2) by.

application of the necessary potential between terminal A and ground,for example, from the pulsing source S, the potential of the grid willbe raised a few volts because of the drop across R1 and R2 and a smallelectron current will flow through the tube. As soon as electrons flowto4 the floating anode, its potential will jump to the second zerovoltage, carrying the grid biasing up to the operatin point. The tubehas then triggered-on or fired, and can be utilized, for example, as anamplifier through the transformers shown.

It can be triggered-oil by decreasing momentarily the potential of thefloating anode to a value slightly less than the first zero value, or bysending a negative pulse into the input or grid circuit, that is,through the transformer T1, of suficient value to momentarily cut offthe electron flow. The triggering pulses to the floating anode in thisfigure are shown as applied through a suitable condenser C1. This tubewhen connected in the proper circuit may be used as a pulse inverting orinverter circuit. Such a circuit is shown in Fig. 4. It comprises twodischarge devices lfi, such as already described. The cathodes areconnected together and to ground, with the deflector plates connected tothe oath-- odes of their respective tubes. Each primary anode isconnected through a load L to the positive terminal of an anodepotential source B, the negative terminal of which is connected toground, and the primary anodes are directly connected through acondenser C30. Each collector grid is connected to its respectiveprimary anode, although it may be connected directly to the potentialsource B, so that its potential does not swing with variations in theelectron currents. The source C of biasing potential for the controlgrids is connected between ground and the junction of resistances P1 andP2, the outer ends of which are connected to the secondary anodes. Thecontrol grids are connected to adjustable or slidable contacts S1, S2engaging with resistances P1, P2. The input circuit conductors 50terminate in an input resistance 66, one endof which is connected toground and the other through condensers 70, iii to the secondary anodeend of the resistances P1, P2. The input terminals 40 may be connectedto any suitable source of electrical pulses of positive polarity.

Let it be assumed that thetube D is fired, that is, that its secondaryanode is at upper zero current potential, and an electron stream ismaintained between the cathode and primary anode; and that tube E isblocked or extinguished. Assume, then, that a positive pulse isimpressed on the terminals 40, and is of such a value that it elevatesthe potential of the secondary anode of tube E above its lowerzero-current potential. As the secondary anode of tube D is alreadyabove that potential, the incoming impulse has little or no effect onthe tube D. The control grid of tube E is driven in the positivedirection, and the tube E is caused to fire in the same way as the tubeof Fig. 3. As the tube E becomes operative, its primary anode swingsnegative, and this negative swing is transmitted by condenser C30 to theprimary anode of tube D decreasing its potential to such an extent thatprimary electrons are no longer enabled to flow in tube D, and thelatter is extinguished. The next positive pulse received at terminals 4%causes tube D to become operative, and causes tube E'to return to itsinitial inoperative condition. Thus, a series of positive pulsestransmitted through the terminals 49 will alternately operable the tubesD, E.

Fig. 5 shows a modification of the circuit of Fig. 4. The essentialdifferences are as follows: The condensers Iii and iii instead of beingconnected to the secondary anodes are connected directly to the controlgrids and the secondary anodes are connected to the positive terminal ofthe battery ,3 through resistances R3. The presence of the resistancesR3 assures that the potential of the secondary anodes will never fallbelow a potential corresponding to the first Zero crossover of Fig. 2,and the circuit as a whole is, therefore, in a condition to have thetubes D and E more readily triggered-on and off. While the circuit ofFig. 4 requires 40 or 58 volts to trigger it, the circuit of Fig. 5 willoperate on pulses of only a fraction of a volt.

What is claimed is:

l. A pulse inverting circuit comprising a plurality of electrondischarge devices, each of said devices comprising a cathode, a controlgrid, a primary anode, and a secondary electron emission anode, meansconnecting said cathodes together, means to cause said devices tooperate in alternation comprising a negative reactance connecting saidprimary anodes, a cathode-primary anode circuit for each deviceincluding load means therein, means for biasing said control grids topreassigned potentials and for initially adjusting said secondary anodesto preassigned poten-,

tials, and means for simultaneously impressing electrical pulses on saidcontrol grids and secondary anodes to cause said devices to bealternately rendered conductive.

2. A pulse generating circuit comprising two electron discharge devices,each of said devices comprising a cathode, a control grid, a primaryanode and a secondary electron emission anode,

means connecting said cathodes together, a cathode-primary anode circuitfor each device including load means therein, means for biasing saidcontrol grids to preassigned potentials for initially adjusting saidsecondary anodes to preassigned potentials, means comprising acapacitance connection between the said primary anodes, and means forsimultaneously impressing electrical impulses on said control grids andsecondary anodes to cause said devices to be alternately renderedconductive.

3. A high vacuum tube trigger circuit comprising two electron dischargedevices, each of said devices comprising a cathode, a control grid, aprimary anode and a secondary electron emission anode, means connectingsaid cathodes together, a capacitance connected between the two primaryanodes, a cathode-primary anode circuit for each device including loa'dmeans therein, means for biasing said control grids to preassignedpotentials and for initially adjusting said secondary anodes topreassigned potentials, a capacitance connection between the twosecondary, anodes, and means for impressing electrical pulses on saidcontrol grids and secondary anodes through said capacitance so that thesaid devices are alternately rendered conductive.

4. A pulse generating circuit comprising two electron discharge devices,each of said devices comprising a cathode, a control grid, a primaryanode and a secondary emission anode, means connecting said cathodestogether, means comprising a negative reactance connecting said primaryanodes, a cathode-primary anode circuit for each device including loadmeans therein, means for biasing said control grids to preassignedpotentials and for initially adjusting said secondary anodes topreassigned potentials, a capacitance connection between the controlgrids, and means for impressing electrical pulses on said control gridsthrough the said capacitance connections.

5. A combination of claim 4 characterized by 6 the fact that there is aresistance connection from each secondary anode to the primary anodevoltage source.

6. A combination of claim 4 characterized by the fact that thecapacitance connection between the control grids comprises twocondensers in series and that the means for impressing electrie calpulses on the control grids is to a point between the two condensers.

7., A combination of claim (l characterized by the fact that thecapacitance connection between the control grids comprises twocondensersin series and that the means for impressing electrical pulseson the control grids is to apoint between the two condensers, and thatthere is a resistance connection from each secondary to the primaryanode voltage source.

8. In combination, a plurality of vacuum electron discharge devices,each of said devices including a pair of electrodes between which anelectron stream may be established, a control electrode between saidelectrodes, and a secondary electron emission electrode for emittingsecondary electrons when said electron stream is established; meansconnected to said control electrodes and to said secondary electrodes,whereby a pulse of positive polarity may be impressed on suchelectrodes; and means to interconnect one of said pair of electrodes inone device to a corresponding one of said pair of electrodes in thesecond device, whereby potential change on either of said interconnectedelectrodes resulting from the establishment of an electron streambetween such electrode and the electrode with which it constitutes onepair of electrodes, reduces the potential on the other of theinterconnected electrodes to a value precluding the maintaining of anelectron stream in the device containing such other electrode.

9. The combination of the next preceding claim in which the meansconnected to the control electrodes and the secondary electrodesincludes a reactance.

10. The combination of claim 8 in which the means connected to thecontrol electrodes and the secondary electrodes includes a negativereactance.

11. The combination of claim 8 in which the means connected to thecontrol electrodes and the'secondary electrodes includes an individualcapacitance for the control and secondary electrodes of each device.

12. The combination of claim 8 in which the means for interconnectingsaid corresponding electrodes of said devices comprises a reactance.

13. The combination of claim 8 in which the means for interconnectingsaid corresponding electrodes of said devices comprises a negativereactance.

to said secondary anodes, whereby a pulse of positive polarity may beimpressed on said grids and secondary anodes; and means to interconnectsaid primary anodes, whereby potential change on one of said anodesresulting from establishment of electron flow between said one anodeandits associated cathode reduces the potential on the other of saidprimary anodes below the value at which an electron stream could bemaintained between said second primary anode and its associated cathode.

15. The combination of next preceding claim in which the meansinterconnecting the primary anodes includes a reactance.

16. The combination of claim 14 in which the means interconnecting theprimary anodes in cludes a negative reactance.

17. The combination of claim 14 in which the means interconnecting theprimary anodes includes'a capacitance.

18. The combination of claim 14 in which the ALBERT SKELLETT. 7

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,043,242 Gebhard June 9, 19362,093,781

Van B. Roberts Sept. 21, 1937

